Cut store bought or home grown heads of Lettuce about 1-2 inches above the root. Place in lettuce farm lid. Then place the lid in a jar of water. Plain water is fine to use however if your going to harvest the lettuce multiple times you may like to use a small amount of liquid nutrients.
To harvest, simply cut the tops off the heads with a pair of scissors about 1-2 inches above the root. The lettuce will continue to grow and produce food for your table.
It takes about two weeks to re-grow your heads of lettuce. And you should be able to harvest it at least 3-5 times before replacing them.
If using very thin heads of lettuce, use a toothpick through the side holes (cut to fit) to help hold very thin lettuce in place till roots start to form.